HitTable

HitTable displays the probability of various outcomes of monsters swinging their swords/axes/fists/claws in your general direction; showing your chance* to be critically hit or be missed, or dodge, parry, or block attacks from monsters 3, 2 and 0 levels above yours.

After installing the addon, you may view the stats by selecting the "Inc. Hit Table" stats panel in the Character frame. You can also use /hits [leveldifference] slash command to view the same statistics using your chat frame.

* Crushing blows not included. Calculations performed on goblin hardware. Diminishing returns of the "to be hit" component of Defense rating are unknown. Do not taunt Happy Fun Rock. Void where prohibited.

[1.2] Fixed issues affecting the calculation of the player's defense skill.
[1.1] Survival of the Fittest talent is now taken into account for druids' chance to be crit.
[1.1] Panel is now shown for all classes.

My Mac runs most all of the add-ons that I have tried, and I would love to get this working.

There's no fundamental difference between windows/osx/wine platforms as far as addons are concerned. The issue more than likely lies in the procedure used to install addons: if WoW is not acknowledging that an addon exists at all after you've restarted the client, you've likely placed it in the wrong directory, or placed the wrong thing in the right directory.

I added this to my system, but it does not show up, even after restarting WoW. Have you done any testing on Macs? My Mac runs most all of the add-ons that I have tried, and I would love to get this working.